Hybrid microstructured optical fibre for guidance by means of photonic forbidden bands and by total internal reflection optimised for non-linear applications

Abstract

The microstructured optical fibre comprises a core ( 4 ) surrounded by a sheath ( 1 ) comprising a base material having a refraction index (ni) and a plurality of at least two different types of inclusion: a first type of inclusion ( 2 ) having a refraction index n2 (n2>n1), and a second type of inclusion ( 3 ) having a refraction index n3 (n3<n1). The inclusions ( 2, 3 ) are arranged and dimensioned in such a way as to ensure guidance, by total internal reflection (RTI), of a fundamental mode of the light, centred on a wavelength λ RTI , and of a fundamental mode of the light in the first photonic forbidden band (BG 1 ), centred on a wavelength λ BG1 , which is different to that λ RTI of the fundamental mode guided by total internal reflection (RTI).

The invention claimed is: 
     
       1. A microstructured optical fibre including a core surrounded by a cladding, the cladding comprising a background material having a refractive index (n1) and several inclusions of at least two different types, a first type of inclusions having a refractive index (n2) that is higher than the refractive index (n1) of the background material, and a second type of inclusions having a refractive index (n3) that is lower than the refractive index (n1) of the background material, said fibre enabling guidance by means of photonic forbidden bands of a fundamental mode of the light, characterized in that the inclusions of the cladding are arranged and dimensioned in such a way as to enable guidance by total internal reflection (RTI) of a fundamental mode of the light, centred on a wavelength λ RTI , and to enable guidance of a fundamental mode of the light in a first photonic forbidden band (BG1), centred on a wavelength λ BG1  that is lower than this wavelength λ RTI  of the fundamental mode guided by total internal reflection (RTI), and wherein the wavelength λ RTI  of the fundamental mode guided by total internal refection (RTI) is situated outside of the wavelength range of the fundamental mode guided in the first forbidden band (BG1). 
     
     
       2. The microstructured optical fibre according to  claim 1 , wherein the average effective index of the cladding is lower than the refractive index (n1) of the background material of the cladding at least for a wavelength range higher than the wavelength λ BG1 . 
     
     
       3. The microstructured optical fibre according to  claim 1 , wherein the core is surrounded by a central crown constituted by the first type of inclusions, all the inclusions of the second type being situated outside of this central crown. 
     
     
       4. The microstructured optical fibre according to  claim 1 , wherein the refractive index (n2) of the inclusions is higher than the refractive index (n4) of the core. 
     
     
       5. The microstructured optical fibre according to  claim 1 , wherein the core of the fibre comprises the same background material as the cladding. 
     
     
       6. The microstructured optical fibre according to  claim 1 , wherein the refractive index (n4) of the cladding is equal to the refractive index (n1) of the background material of the cladding. 
     
     
       7. The microstructured optical fibre according to  claim 6 , wherein the core of the fibre is constituted of the same material as the background material of the cladding. 
     
     
       8. The microstructured optical fibre according to  claim 1 , wherein the inclusions are arranged in the form of a periodic network characterized by a constant step. 
     
     
       9. The microstructured optical fibre according to  claim 8 , wherein the dimension of the second type of inclusions and the step of the network of inclusions are chosen in such a way that the average effective index of the cladding is lower than the refractive index (n1) of the background material of the cladding at least for a wavelength range that is higher than the wavelength λ BG1 . 
     
     
       10. The microstructured optical fibre according to  claim 1 , wherein the inclusions of the cladding are arranged and dimensioned in such a way as to allow a combination of m waves (m≧3) that are phase-matched, with at least two of these waves possessing different wavelengths (λ RTI , λ BG1 ), belonging respectively to the fundamental mode guided by total internal reflection (RTI) and to the fundamental mode guided in the first photonic forbidden band (BG1). 
     
     
       11. The microstructured optical fibre according to  claim 1 , wherein the fundamental mode guided in the first forbidden band (BG1) and the fundamental mode guided by total internal reflection (RTI) cumulatively respect the following conditions (a) and (b): 
       
         
           
             
               
                 
                   
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         m 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         1 
                         
                           λ 
                           i 
                         
                       
                     
                     = 
                     0 
                   
                 
                 
                   
                     ( 
                     a 
                     ) 
                   
                 
               
               
                 
                   
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         m 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           n 
                           
                             λ 
                             i 
                           
                         
                         
                           λ 
                           i 
                         
                       
                     
                     = 
                     0 
                   
                 
                 
                   
                     ( 
                     b 
                     ) 
                   
                 
               
             
           
         
         m being a whole number above or equal to 3, and n λi  being the value of the effective index of the fundamental mode propagated in the optical fibre at wavelength λ i , 
         and in that of the wavelengths λ i  that respect the conditions (a) and (b), at least one wavelength (λ RTI ) belongs to the fundamental mode guided by total internal reflection (RTI), and at least one wavelength (λ BG1 ) belongs to the fundamental mode guided in the first forbidden band (BG1). 
       
     
     
       12. The microstructured optical fibre according to  claim 1 , wherein the inclusions of the cladding are arranged and dimensioned in such a way that for at least two different wavelengths λ RTI  and λ BG1  belonging respectively to the fundamental mode guided by total internal reflection (RTI) and to the fundamental mode guided in the first photonic forbidden band (BG1), the effective refractive indices of the fibre at these two wavelengths λ RTI  and λ BG1  are equal and lower than the refractive index (n1) of the background material of the cladding. 
     
     
       13. The microstructured optical fibre according to  claim 1 , wherein the two wavelengths λ RTI  and λ BG1  respect the following condition: λ RTI =k·λ BG1 , k being a whole number above or equal to 2. 
     
     
       14. The microstructured optical fibre according to  claim 13 , wherein the two wavelengths λ RTI  and λ BG1  respect the following condition: λ RTI =2λ BG1 . 
     
     
       15. The microstructural optical fibre according to  claim 13 , wherein the two wavelengths λ RTI  and λ BG1  respect the following condition: λ RTI =3λ BG1 . 
     
     
       16. The microstructured optical fibre according to  claim 1 , wherein the network of inclusions is hexagonal and of the honeycomb type. 
     
     
       17. The microstructured optical fibre according to  claim 1 , wherein the network of inclusions forms a square. 
     
     
       18. The microstructured optical fibre according to  claim 1 , wherein the network of inclusions includes at least two concentric crowns formed by inclusions of the first type, each inclusion of the first type being surrounded by several inclusions of the second type, with the exception of inclusions of the first type of the central crown. 
     
     
       19. The microstructured optical fibre according to  claim 1 , wherein the background material of the cladding is made of silica and the inclusions of the second type include air holes. 
     
     
       20. The microstructured optical fibre according to  claim 1 , wherein the background material of the cladding is made of silica and the inclusions of the first type include inclusions of doped silica. 
     
     
       21. The microstructured optical fibre according to  claim 20 , wherein the inclusions of the first type include inclusions made of silica doped with germanium or of silica doped with phosphorus. 
     
     
       22. The microstructured optical fibre according to  claim 1 , wherein the background material of the cladding is made of silica and the inclusions of the first type include inclusions made of tellurite glass or of chalcogenide glass. 
     
     
       23. The microstructured optical fibre according to  claim 1 , wherein the inclusions of the first type include inclusions containing a liquid or gas presenting a refractive index (n2) higher than the refractive index (n1) of the background material of the cladding. 
     
     
       24. The microstructured optical fibre according to  claim 1 , wherein the inclusions of the second type include inclusions containing a liquid or gas presenting a refractive index (n3) lower than the refractive index (n1) of the background material of the cladding. 
     
     
       25. Use of a microstructured optical fibre as described in  claim 1  for the generation of frequencies by non-linear effects, in particular for one of the following applications: the generation of twin photons, the generation of triplet photons, and the generation of multiple frequencies, in particular the doubling of frequency and the tripling of frequency. 
     
     
       26. A microstructured optical fibre including a core surrounded by a cladding, the cladding comprising a background material having a refractive index (n1) and several inclusions of at least two different types, a first type of inclusions having a refractive index (n2) that is higher than the refractive index (n1) of the background material, and a second type of inclusions having a refractive index (n3) that is lower than the refractive index (n1) of the background material, said fibre enabling guidance by means of photonic forbidden bands of a fundamental mode of the light, characterised in that the inclusions of the cladding are arranged and dimensioned in such a way as to enable guidance by total internal reflection (RTI) of a fundamental mode of the light, centred on a wavelength λ RTI , and to enable guidance of a fundamental mode of the light in a first photonic forbidden band (BG1), centered on a wavelength λ BG1  that is lower than this wavelength λ RTI  of the fundamental mode guided by total internal reflection (RTI), wherein the fundamental mode guided in the first forbidden band (BG1) and the fundamental mode guided by total internal reflection (RTI) cumulatively respect the following conditions (a) and (b): 
       
         
           
             
               
                 
                   
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         m 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         1 
                         
                           λ 
                           i 
                         
                       
                     
                     = 
                     0 
                   
                 
                 
                   
                     ( 
                     a 
                     ) 
                   
                 
               
               
                 
                   
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         m 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         
                           n 
                           
                             λ 
                             i 
                           
                         
                         
                           λ 
                           i 
                         
                       
                     
                     = 
                     0 
                   
                 
                 
                   
                     ( 
                     b 
                     ) 
                   
                 
               
             
           
         
       
       m being a whole number above or equal to  3 , and n λi , being the value of the effective index of the fundamental mode propagated in the optical fibre at wavelength λ i , and in that of the wavelengths λ i  that respect the conditions (a) and (b), at least one wavelength (λ RTI ) belongs to the fundamental mode guided by total internal reflection (RTI), and at least one wavelength (λ BG1 ) belongs to the fundamental mode guided in the first forbidden band (BG1). 
     
     
       27. Use of a microstructured optical fibre as described in  claim 26  for the generation of frequencies by non-linear effects, in particular for one of the following applications: the generation of twin photons, the generation of triplet photons, and the generation of multiple frequencies, in particular the doubling of frequency and the tripling of frequency. 
     
     
       28. A microstructured optical fibre including a core surrounded by a cladding, the cladding comprising a background material having a refractive index (n1) and several inclusions of at least two different types, a first type of inclusions having a refractive index (n2) that is higher than the refractive index (n1) of the background material, and a second type of inclusions having a refractive index (n3) that is lower than the refractive index (n1) of the background material, said fibre enabling guidance by means of photonic forbidden bands of a fundamental mode of the light, characterised in that the inclusions of the cladding are arranged and dimensioned in such a way as to enable guidance by total internal reflection (RTI) of a fundamental mode of the light, centred on a wavelength λ RTI , and to enable guidance of a fundamental mode of the light in a first photonic forbidden band (BG1), centred on a wavelength λ BG1  that is lower than this wavelength λ RTI , of the fundamental mode guided by total internal reflection (RTI), wherein the two wavelengths λ RTI  and λ BG1  respect the following condition: λ RTI  =k·λ BG1 , k being a whole number above or equal to 2. 
     
     
       29. Use of a microstructured optical fibre as described in  claim 28  for the generation of frequencies by non-linear effects, in particular for one of the following applications: the generation of twin photons, the generation of triplet photons, and the generation of multiple frequencies, in particular the doubling of frequency and the tripling of frequency.